The invention relates to clutches and components thereof. In particular, but not exclusively, the invention relates to carbon/carbon clutches especially for high performance vehicles such as racing cars.
It is known to provide carbon/carbon clutches comprising a series of inner and outer plates or discs consisting of carbon/carbon. Such clutch plates are particularly beneficial in providing a lightweight clutch and an increasing coefficient of friction with temperature. However, carbon is also known to have a low shear modulus and accordingly it is important to take great care in transferring drive to the series of driving plates (either of the inner or outer clutch plates) in order to mitigate against failure at the interface between the drive shaft (or other driving means) and the driving plates. Furthermore, it is important to ensure even wear across the different interfaces between the series of outer and the series of inner clutch plates in order to optimise the use of the clutch.
Accordingly, the invention seeks to address these issues and to provide an improved clutch thereby avoiding or at least mitigating these and other problems in the prior art.
Accordingly, a first aspect of the invention provides a hub assembly for a carbon/carbon clutch comprising a hub, a first clutch plate, and retaining means or locator releasably attachable to the first clutch plate thereby axially to fix the first clutch plate with respect to the hub. Preferably the retaining means or locator is readily and/or mechanically releasably attachable to the first clutch plate and preferably still the assembly comprises a threaded bolt or rivet to releasably attach the retaining means to the first clutch plate.
Preferably the retaining means is releasably attachable to the hub, and more preferably is mechanically releasably attachable to the hub. Preferably still the assembly comprises a threaded bolt to releasably attach the retaining means to the hub.
Preferably the hub comprises two or more, and more preferably three or five, circumferentially spaced apart groups of teeth which teeth radially protrude from the hub. Preferably each group comprises two or more teeth, and more preferably 4 or 8 teeth.
In some embodiments of the invention the spacing between an adjacent group of teeth is substantially the size of an individual tooth.
Preferably the spacing between an adjacent group of teeth is adapted to receive an axial protrusion on the first clutch plate.
Preferably the retaining means comprises a retaining ring having an annular body and more preferably also comprises one or more apertures adapted to co-operate with locking means thereby to attach the retaining means to the first clutch plate. Preferably still the retaining ring comprises a series of circumferentially evenly spaced apertures and/or the first clutch plate comprises a series of spaced means to enable releasable attachment to the retaining ring. Preferably the first clutch plate comprises a series of circumferentially evenly spaced apertures adapted to register with a series of apertures in the retaining ring thereby to enable attachment of the first clutch plate and retaining ring for example by riveting. More preferably the assembly comprises a separate sleeve for each of the apertures in the first clutch plate.
Alternatively or additionally the retaining means comprises one or more tabs and preferably each tab comprises one and preferably two apertures.
Preferably the first clutch plate, and preferably still two or more clutch plates, comprise(s) a series of circumferentially spaced groups of recesses adapted to engage teeth on the hub. More preferably an aperture is provided in a spacing in the first clutch plate between an adjacent pair of groups of recesses.
A carbon/carbon clutch can be provided comprising a hub assembly according to the first aspect of the invention.
According to a second aspect of the invention there is provided a hub for a carbon/carbon clutch comprising a splined central aperture and a series of circumferentially spaced and radially protruding teeth, wherein the teeth are clustered in two or more, and preferably three or five, spaced apart groups. Preferably each group comprises two or more teeth and more preferably 4 or 8 teeth.
Preferably the teeth are substantially parallel sided.
Preferably one tooth in each group is wider than the other teeth in the group and preferably one tooth in each group comprises a threaded bore. More preferably the same tooth in each group is wider and has a threaded bore.
Preferably the first clutch plate and hub comprise co-operating drive elements and wherein the assembly is configured such that the retaining means or locator does not pass any rotational drive between the first clutch plate and hub in use.
Preferably the invention comprises a drive prevention mechanism or means which enables relative circumferential movement of the retaining means with respect to at least one of the first clutch plates and the hub. More preferably the drive prevention means comprises a fixing element, which preferably comprises a sleeved rivet, which cooperates with the retaining means and first clutch plate, and is retained in an aperture in one of the retaining means and first clutch plate which aperture is significantly larger than the fixing element to enable circumferential movement between the first clutch plate relative to the retaining means.
According to another aspect of the invention there is provided a clutch plate for a carbon/carbon clutch comprising a central aperture for receiving a toothed hub, and a series of recesses each recess being adapted to co-operate with a hub tooth thereby to enable the clutch plate to be driven, wherein the recesses are clustered into two or more spaced apart groups.
Preferably the clutch plate comprises a series of evenly spaced means to enable releasable attachment of a retaining ring to the first clutch plate.
Preferably the clutch plate comprises a series of circumferentially evenly spaced apertures adapted to register with a series of apertures in the retaining ring thereby to enable attachment of the first clutch and retaining ring for example by riveting and more preferably there is provided a separate sleeve for each of the apertures in the clutch plate.
According to yet another aspect of the invention there is provided a hub assembly for a carbon/carbon clutch comprising a clutch plate and hub adapted to drive the clutch plate rotationally about a central longitudinal axis thereof, and means for axially locating the clutch plate on the hub which axial location means is independent and/or separable from the hub.
Preferably the hub contacts two or more clutch plates.